Mode Of Heat Transfer Research Articles

Heat transfer software for local materials in Cameroon (HTSLM 1.0): simplified building energy software based on local realities

We report in this work the overall design of a software application for calculating the indoor temperature in a room of a building constructed from local materials in Cameroon based on heat transfer modes. This software is intended to be simplified and at a lower cost for the user. We dubbed it LOBATIN/HTSLM 1.0 for the first release. We describe the physical modeling background based on the stationary aspect of the transfer of heat flow via conduction, convection and radiation from the outside to the inside of the supposedly uninhabited building. We present how we manage Cameroon’s meteorological data to implement them in LOBATIN/HTSLM 1.0 and we compare our results with pre-existing software such as EnergyPlus. The curves obtained for hourly indoor temperatures for the chosen days in the five climatic zones defined for the software, all show a realistic bell-shaped evolution, thus prefiguring a digital decision support tool for such admitted infrastructures to be made of materials from the Local Materials Promotion Authority of Cameroon.

Low Thermal Conductivity and Diffusivity at High Temperatures Using Stable High-Entropy Spinel Oxide Nanoparticles.

The realization of low thermal conductivity at high temperatures (0.11W m-1 K-1 800 °C) in ambient air in a porous solid thermal insulation material, using stable packed nanoparticles of high-entropy spinel oxide with 8 cations (HESO-8 NPs) with a relatively high packing density of ≈50%, is reported. The high-density HESO-8 NP pellets possess around 1000-fold lower thermal diffusivity than that of air, resulting in much slower heat propagation when subjected to a transient heat flux. The low thermal conductivity and diffusivity are realized by suppressing all three modes of heat transfer, namely solid conduction, gas conduction, and thermal radiation, via stable nanoconstriction and infrared-absorbing nature of the HESO-8 NPs, which are enabled by remarkable microstructural stability against coarsening at high temperatures due to the high entropy. This work can elucidate the design of the next-generation high-temperature thermal insulation materials using high-entropy ceramic nanostructures.

Transient Thermal Simulation of Lithium‐Ion Batteries for Hybrid/Electric Vehicles

This paper focuses on the development of a plug‐in hybrid vehicle (PHEV) full‐vehicle transient thermal model in thermal modelling software to predict the battery surface temperature at various locations. The full‐vehicle thermal model consists of a full exhaust piping system, a high‐voltage lithium‐ion battery pack system, and a battery liquid coolant system. All modes of heat transfer including conduction, forced and natural convection, radiation from the exhaust system, battery cooling, and battery internal heat generation are considered in the model. The full‐vehicle model is simulated under various vehicle conditions to represent four standard customer drive cycles. The simulated battery surface temperature at specified points along the battery module surfaces is compared to experimental vehicle test‐cell data to provide model validation. Using the results from the transient thermal simulations, prediction of the battery thermal degradation is performed throughout the entire vehicle lifecycle. The thermal degradation is estimated using thermal goals and equivalent exposure times.

An internal/external dual heat transfer mode constructed by femtosecond-laser direct writing for enhancing water boiling in graphene oxide surface

An internal/external dual heat transfer mode constructed by femtosecond-laser direct writing for enhancing water boiling in graphene oxide surface

Comparing the improvement of occupant thermal comfort with local heating devices in cold environments

Local heating can improve the thermal comfort of occupants and save energy in buildings in cold environments; however, few studies have investigated the effects of heat-transfer modes. Here, we aimed to evaluate different local heating measurements including five-sided enclosed radiant panel, heating plate, and fan heater using climate chamber experiments with 20 participants in cold environments (14 °C). Skin temperature and thermal perception votes under two radiation types with low and high power, one condition of conduction, and one condition of convection were collected and analyzed (RL, RH, CD, and CV). Under conditions RH, CD, and CV, the investigated parameters significantly improved by three local heating devices, with foot skin temperature rising by 0.46 °C, foot thermal sensation rising by 1.25 scores, and overall thermal comfort increasing by 0.36 score; however, their energy consumption varied greatly. In contrast, no significant improvement was observed in the RL group. Additionally, direct application of heat at sites of palpable cold discomfort was not always the optimal approach, and heating other parts of the body may provide significant alleviation. We recommend that the surface temperature of local heaters based on conduction and radiation for heat transfer should not be lower than 40.38 °C and 52.15 °C, respectively. To maintain thermal comfort, air outlet temperature should not be lower than 34.56 °C for convection type heaters. Our results provide technical and experimental basis for designing energy-saving buildings.

Investigating Thermal Performance of Substrate Board through Forced Convection and Machine Learning

In this study, the thermal performance of substrate board exposed to forced convection with different heat source configurations was investigated. Seven asymmetric integrated circuit chips (heat sources) positioned at various points on the substrate board were cooled through steady-state experiments using laminar forced convection heat transfer mode. The objective was to determine the optimal layout of the seven integrated circuit chips on the board for lowering the maximum temperature. The optimal configuration was determined experimentally and was further validated by employing a machine-learning optimization strategy. Various correlations have been proposed to investigate the effect of the substrate board arrangement on the integrated circuit (IC) Chip temperature and heat transfer coefficient. These findings imply that the size and configuration of the substrate board, input heat flux, and placement of the IC chips have a significant impact on their temperature. Because the heat is discretely placed in this scenario, the temperature of the integrated circuit (IC) chips is the lowest for higher values of the non-dimensional parameter λ. This aids in efficiently reducing the temperature of chips through cooling. Another important factor in the cooling of IC chips is air velocity. The maximum temperature reduction is 14.02% at an air velocity of 3.5 m/s.

Three-stage Lobatto analysis on hydrodynamic Eyring-powell flow of nanofluid: Impact of viscous dissipation, thermal radiation, and wall slip dynamics

Thermal radiation and viscous dissipation play crucial roles in the phenomenon of boundary layer flow, especially in engineering and industrial applications involving high temperatures, such as in combustion engines, gas turbines, and furnaces, thermal radiation becomes a significant mode of heat transfer whereas viscous dissipation signifies the conversion of kinetic energy into thermal energy due to the frictional forces in the fluid. The key findings of the current investigations is to explore 3D magneto-hydrodynamics radioactive Eyring-Powell nanofluid flowing towards a stretchable porous surface using a three-stage Lobatto numerical. The influence of velocity and thermal slip under convective boundary constraints are also incorporated in the present investigations. The Eyring-Powell model, known for its relevance in non-Newtonian fluid mechanics, is used to simulate a nanofluid's flow dynamics and heat transfer characteristics. The mathematical Navies-Stokes equations are transformed into a system of ordinary differential equations (ODEs) by adopting a similarity variable, which are then solved numerically with the aid of the MATLAB bvp4c package. Results highlight the significance of physical parameters involved in the model like magnetic field strength , slip parameter, Eckert number, Lewis number, thermophoresis parameter, Brownian motion parameter and their impact on velocity temperature, and concentration profiles are displayed in the form of graphically. The data reveals an 11.2% increase in the heat transfer rate and a 6.65% increment in mass transfer when the radiation parameter is raised from 0.1 to 0.4. Results also elucidate that fluid temperature at the boundary rises as the Biot number increases because the rate of heat transfer between a solid surface and the surrounding fluid becomes more efficient. To check the validity and reliability of the present study, our calculated results are compared with the previous one, which shows stable agreement.

Exploration of the reactivities of homemade binary pyrotechnics

Understanding the properties of explosives is the basis for investigating and analyzing explosion cases. To date, due to the strict legal control of standard explosives and initiators, homemade pyrotechnics composed of oxidizers and fuels have become popular explosive sources of improvised explosive devices (IEDs) threatening greatly social stability and personal safety. The reactivity of pyrotechnics strongly depends on their intrinsic characteristics and operating conditions, which determine the efficiencies of heat and mass transfer between the reaction zone and the unreacted zone. Herein, the tests of thermodynamics, pressurization characteristics, and combustion propagation behaviors are conducted to explore the effects of oxidizer species, particle size, and loading density on the reactivity of homemade binary aluminum-based pyrotechnics. The results show that the pyrotechnics with potassium chlorate (KClO3) have the strongest reactivity with the highest pressurization rate (dp/dt) and the shortest combustion duration. Compared with their counterparts based on aluminum microparticles(mAl), pyrotechnics consisting of Al nanoparticles (nAl) possess superior reactivity as expected, which results from the relatively short heat and mass transfer distances. The nAl-based pyrotechnics have a low reaction exothermic peak temperature, great heat release, great aluminothermic reaction completeness, and high produced peak pressure with several orders of magnitude higher pressurization rate. Increasing the loading density of the pyrotechnics over a certain value can change the dominant mode of heat transfer from convective to conduction, sharply decreasing the pressurization characteristics and combustion front propagation velocities (vp). The results of theoretical calculations using the NASA-CEA codes show that loading density can alter the reaction process of the pyrotechnics, leading to a decrease in the predicted pressure per unit mass for Al/KNO3 or Al/AP, and an increase for Al/KClO3. For nAl/potassium nitrate (KNO3), the density is between 1.0 and 1.25 g cm−3, across which dp/dt decreases by one order of magnitude from 0.148 to 0.014 MPa ms−1. In addition, vp decreases by three orders of magnitude from 0.040 to 0.078 m s−1. Distinct pressurization behaviors of nAl/AP are observed at a density of 1.5 g cm−3, while the variation in nAl/KClO3 reactivity fluctuates. These results are beneficial for the damage assessment of scenes caused by an explosion and for inversely calculating charge parameters.

Flow field and heat transfer in the transitional type of turbulent round jet impingement

Jet impingement heat transfer in the transitional type involves the occurrence and disappearance of the secondary maximum heat transfer, which is challenging for numerical simulation. In the paper, the effects of the nozzle-plate spacing H/D on heat transfer and flow fields in the range of 5≤H/D≤7 within the transitional type are investigated. In this type, the secondary maximum heat transfer rate gradually vanishes. In addition, the transitional properties of jet impingement are further discussed. It is found that the heat transfer rate at the stagnation point shows an important relationship with the arriving stream Reynolds number and turbulence intensity. Additionally, three heat transfer modes, i.e., the peak (5<H/D≤5.5), swelling (5.5<H/D≤6.6), and linear modes (6.6<H/D≤7), are identified in the transitional type based on the analysis of the heat transfer rate, development of the intermittency, and the wall shear stress. For the latter two aspects, the laminar zone and the turbulence zone are discussed in detail for different H/D. In the peak mode, heat transfer rate is largely influenced by the transition process, resulting in a secondary peak. While in the swelling mode, the second peak evolves to a swelling and the effect of transition becomes weak. As a result, the influences of the laminar region will extend to downstream. However, in the linear mode, the swelling vanishes with a mild change of intermittency in the boundary layer and the sudden mutation of heat transfer mainly takes place in the stagnation region.

Experimental study on the low-temperature preheating performance of positive-temperature-coefficient heating film in the prismatic power battery module

The performance of a power battery directly affects the thermal safety performance of the vehicle. Aiming at the improvement of thermal safety of lithium-ion batteries under low temperature condition, this study focuses on the effect of the positive-temperature-coefficient (PTC) heating film on the heating performance of batteries through experimental testing. First, the side and bottom of the cell were heated, and the heat transfer path and mode of the single cell were analyzed. The effects of different power densities and geometric positions on the heating effect were studied by testing the heating time and temperature consistency. Second, for the battery module, a low-temperature heating thermal management heat transfer model was built to analyze the heating mechanism of the heating film under different heating power densities. Finally, the results of these studies were synthesized to obtain the optimal heating power density. The results show that for the cell, the optimum power density of side heating and bottom heating is 0.5 W /cm2 and 0.4 W /cm2, respectively. The time required for side heating from −20 °C to 10 °C is 730 s lower than that of bottom heating, and the maximum temperature difference is 1.885 °C lower. For battery modules, a power density of 0.5 W/cm2 was appropriate for both bottom and side heating methods. Due to the existence of heat conduction between battery packs, the battery modules will be quickly and evenly preheated. Under the optimal power density, the time length for side heating from –20 °C to 10 °C was 1459 s, and the maximum temperature difference was 6.32 °C; bottom heating time required slightly more time (1783 s), and the maximum temperature difference was 6.221 °C. Side heating can be beneficial for the rapid preheating of the battery module. This study will contribute to improving the performance and safety of batteries in cold environments.

Characteristics and Efficiency of Heat Transfer for Natural Convection by Ag-CuO/H2O Hybrid Nanofluid Inside a Square Cavity with Corrugated Walls

A parametric numerical study is conducted on laminar natural convection and heat transfer in a cavity with opposing undulated walls saturated with a hybrid Ag-CuO/water nanofluid. The two vertical walls of the sinusoidally undulated cavity are maintained at hot and cold temperatures, while the upper and lower walls are thermally insulated. The investigation examines the effects of relevant parameters such as the sinusoidally undulated geometry of the walls for different volumetric fractions of nanoparticles (0% ≤φ≤6%) and Rayleigh numbers (103 ≤ Ra ≤ 106) Thefinite-volumee discretization method is employed to solve the system of governing equations. The results indicate that an increase in the volumetric fraction of nanoparticles enhances the heat exchange rate in the cavity. Additionally, the Rayleigh number, with a significant increase in surface area, strongly influences the dominant heat transfer mode in the cavity. Furthermore, an increase in the number of wall undulations leads to a reduction in the heat transfer rate.

Application of LED Bulb with Perforated Plus Shape Fin Array in Mines

This paper works on design and developments of cooling system of LED. This work particularly studies on the passive cooling system of a 50W street-light lamp made by multiple LEDs. For analysis purposes, different parameters are considered such as: Density, kinematic viscosity, velocity, junction temperature, heat transfer rate, laminar flow and heat transfer modes. The findings suggest that using plus shape fins with a 1 mm diameter drill can enhance convection heat transfer, resulting in a 21.8% increase in surface area. Additionally, the "Plus" shape of the fins facilitates the formation of an air swirl, contributing to a 30.41% decrease in heat sink temperature. Furthermore, material porosity enhances cooling rates by generating swirls and promoting upward airflow. Ultimately, Plus shape fins emerge as an optimal solution for passive cooling systems, mimicking the efficiency of active cooling systems. The cooling model, proposed along with different shapes and weights of materials having specially designed fins porous materials, is unique so far in our knowledge.

A hybrid experimental configuration for emissivity measurement at cryogenic temperatures

Abstract In cryogenic and high vacuum systems, radiation mode of heat transfer is the primary source of energy interaction owing to the wide temperature differentials and very low temperatures and pressures. Measurement of radiative properties such as emissivity is crucial in the design of cryogenic systems. Emissivity measurement at cryogenic temperatures requires careful consideration of the sample preparation and measurement conditions to ensure accuracy and reliability. Most experimental techniques developed so far are complex in their design and equipment, and they work only on a single measuring method. To address these challenges, this research has proposed a simpler and hybrid experimental setup that could employ both calorimetric and heat flux methods to directly measure the total hemispherical emissivity in the range 90 K–180 K. Experiments were conducted with five types of materials (black paint, stainless steel, aluminum foil, aluminized mylar foil, and copper sheet) by using both methods, and the results were validated with the literature data. The data obtained by calorimetric and heat flux methods for each sample showed a high level of consistency with each other, with a variation of only ±1.5%. Moreover, the discrepancy between the measured and literature data was within the acceptable range of 0.3%–10%. The total hemispherical emissivity of mechanically treated copper was higher than that of chemically polished copper by 11%. This simplified setup has incorporated all possible means to minimize heat leakages into and from the cryostat while maintaining accuracy. The obtained data can be used to accurately estimate the radiation heat loads in cryopumps and other cryogenic systems that use similar components.

Analysis and optimization of dynamic and static thermal rectification in shell-and-tube phase change thermal rectifiers

Thermal rectification devices based on solid-liquid phase change material (PCM) can realize efficient and reversible control of forward and reverse heat flux. In this study, an analytical solution for a shell-and-tube phase change thermal rectifier is derived based on Fourier's law of heat conduction. The validity of the analytical model is confirmed by the numerical model verified by the exact solution of the single-phase Stefan problem. The influence of thermophysical properties, structural parameters, and initial temperature on the dynamic and static thermal rectification effects of the shell-and-tube heterojunction composed of polydimethylsiloxane (PDMS) and hexadecane (C16) is investigated and optimized. Results indicate that the proposed analytical model for the shell-and-tube phase change thermal rectifier enables rapid and precise prediction of thermal rectification effects. The presence of solid-liquid phases of C16 under forward and reverse heat transfer modes reduced the thermal resistance difference, resulting in poor initial rectification performance (only about 1.17). The optimized thermal rectification effect is significantly increased to 1.56, which is significantly improved by 33.56 %. Moreover, the dynamic rectification effect of the shell-and-tube thermal rectifier is notably higher than the static rectification effect. The average dynamic thermal rectification ratio within the first 50 s before and after optimization is 2.19 and 7.80, respectively, which is several times higher than the static thermal rectification ratio. This paper further analyzes the impact of initial temperature and finds that an increase in initial temperature can further enhance the dynamic thermal rectification effect. Raising the initial temperature to 5 K above the phase change temperature can increase the improvement of the dynamic rectification effect to 256.36 % in the first 50 s. The significance of this study lies in its potential to advance the understanding and practical application of thermal rectification based on PCM.

Experimental and numerical investigation of heat transfer modes on pot surfaces in a power range of a cooking porous burner

The investigation of convective and radiative heat transfers to a cooking pot in a porous burner, coupled with an analysis of the pot's bottom and side contributions to total heat transfer, remains an underexplored area of research. In this study, we adopt a comprehensive approach, combining experimental measurements and 3D numerical models, to explore the practical application of a Silicon carbide porous burner fueled with natural gas in cooking pots with power ranging from 12.15 kW to 31.04 kW. Three primary aspects are examined: differentiating between radiative and convective heat transfer contributions, investigating porous mixing characteristics, and analyzing the burner's thermal and combustion efficiencies. To facilitate this investigation, a dedicated test bench is meticulously designed and constructed, equipped with state-of-the-art measuring instruments to effectively monitor the thermal behavior of the heating process. The results reveal that the higher Damköhler number at higher power, driven by the dominance of chemical time over mixing time, accentuates the importance of chemical reactions in heat transfer to the pot. Moreover, increasing the power leads to a reduction in the burner's overall thermal efficiency, from 29.2% to 18.8%, due to a higher energy waste percentage, escalating from 45.12% at P = 12.15 kW to 65.31% at P = 31.04 kW. This increase in power also strengthens the downward movement of the flame and its detachment from the pot surface. The pot's bottom contribution to total heat transfer ranged from 76.7% to 95.5%, with convection alone accounting for over 98% in all cases. Consequently, optimizing the pot bottom geometry for the purpose of enhancing convection presents promising avenues for significantly boosting thermal efficiency. These findings highlight the potential of the investigated porous burner for efficient and clean combustion in cooking appliances.

Energy and exergy analysis of a multipass macro-encapsulated phase change material/expanded graphite composite thermal energy storage for domestic hot water applications

This study presents the development and performance evaluation of an innovative thermal energy storage (TES) system utilizing a commercially available bioderived organic phase change material (PCM) for domestic hot water production. The primary objective of this research is to enhance the efficiency and effectiveness of thermal energy storage solutions by macro-encapsulating the PCM-expanded graphite (EG) compressed modules in a multi-pass tube arrangement. A comprehensive experimental setup was employed to investigate the thermal performance of the proposed TES unit, focusing on charging and discharging cycles. Key findings reveal that conduction is the dominant mode of heat transfer, with the system achieving a significant maximum average charging power of 1440 W and a discharging power of 1990 W. The thermal energy storage capacity reached an impressive 12.6 MJ, enabling the discharge of 90 % of stored energy within 90 min. Furthermore, the exergy analysis indicated high exergy efficiencies, with charging efficiencies reaching 98 % and overall exergy efficiency at 18 %.The implications of this research are significant, demonstrating the feasibility of using bioderived organic PCM for sustainable energy applications. It highlights the potential of the modular structure of the system to integrate with heat pump and solar energy systems, thereby enhancing efficiency and sustainability in domestic hot water applications. This work significantly contributes to the advancement of sustainable thermal energy storage technologies and establishes a solid foundation for future studies aimed at optimizing TES systems for domestic hot water production.

Analysis of heat transfer modes in the cooling of blocks generating different heat quantities

Achieving improved cooling efficiency and control in electronic components with varying heat outputs can be realized through a thorough analysis of different heat transfer modes, focusing on their contributions and interactions within the system. The analysis is conducted within a cavity containing three circular blocks generating varying amounts of heat. The blocks are affixed to an insulated plate, dividing the cavity into two identical sections with different fluids and different cooling mechanisms. In the open portion of the divided cavity, block cooling is achieved through forced convection using a nanofluid, while the closed section dissipates heat through natural convection and surface radiation. The numerical solution of the governing equations is performed using Galerkin's Finite Element Method, with detailed examination of the cooling process considering various parameters, such as block displacement (1.5cm≤y1≤3.25cm) and dimensions (0.25cm≤R≤1.5cm), Reynolds number (10≤Re≤1000), nanoparticles nature and volumetric fraction(0 %–10 %), emissivity (0≤ε≤1), thermal heat ratio(0.125 to 8), and cavity inclination angle(0°–180°). The results show that the combination of natural convection and surface radiation can be highly effective, rivaling forced convection in cooling the blocks. The study shows that an increase in the Reynolds number results in a temperature reduction of up to 6 °C, while increasing the emissivity leads to a more significant drop of around 10 °C. Additionally, miniaturizing the blocks by reducing their radius by a factor of six causes the maximum temperature to rise by over 20 °C.

Modulation of radiative heat transfer by higher-order topological phonon polaritons

Modulation of radiative heat transfer by higher-order topological phonon polaritons

Numerical Investigation on the Influence of Substrate Board Thermal Conductivity on Electronic Component Temperature Regulation

This study presents a detailed numerical analysis of substrate boards made from various materials (FR-4, Si cladding, and Cu cladding) with nine electronic components mounted on them. Each component is subjected to different heat fluxes, and the analysis covers both natural convection (NC) and forced convection (FC) modes of heat transfer at air velocities of 4m/s and 6m/s. The findings reveal that at an air velocity of 6m/s, using a copper cladding board significantly lowers the temperatures of the electronic components by 340C to 540C compared to FR-4 and Si cladding boards. Additionally, the copper cladding reduces the required air-cooling velocity by 2m/s and achieves a temperature reduction for the IC chips ranging from 3.500C to 13.120C. It is recommended to use an air velocity of 4m/s with copper cladding to minimize fan power consumption while maintaining component temperatures below 1250C. These results provide crucial insights for thermal design engineers, aiding in the selection of appropriate substrate boards for effective thermal management of electronic components. The study emphasizes the benefits of copper cladding in distributing heat more uniformly, reducing energy consumption, and maintaining optimal operating temperatures. Furthermore, it suggests that placing high heat-dissipating components at inlet or outlet points can minimize thermal interactions and overall configuration temperatures. The research offers valuable guidance to the heat transfer community, particularly electronic thermal designers, by highlighting the importance of substrate material choice and component placement in enhancing the reliability and lifespan of integrated circuits (ICs). The comprehensive analysis and recommendations serve as a vital resource for optimizing thermal control strategies in electronic devices, ultimately contributing to improved performance and durability.

Thermal Performance Evaluation of a Single-Mouth Improved Cookstove: Theoretical Approach Compared with Experimental Data

This work aims to address the knowledge gap in the thermal efficiency performance of a locally made cookstove in Mali. Despite the fact that the thermal efficiency of cookstoves is a crucial aspect of cooking, the performance of commercially produced cookstoves in Mali has not been thoroughly studied. In this context, the thermal efficiency of a single-mouth biomass stove has been investigated using a theoretical and experimental approach. First, the fundamental principles of physics for the three forms of heat transfer were applied. Then, the theoretical thermal efficiency of the stove was calculated based on the percentage share of energy gains and losses for the respective heat transfer modes. This analysis shows that the highest energy gain is achieved by radiation heat transfer from the flame and the fuel bed, followed by convection heat transfer to the bottom and sides of the pot, respectively. In order to validate the findings, the theoretical results have been compared with the experimental data at a case study site in Katibougou, Mali. Accordingly, the experimental thermal efficiency is slightly lower than the theoretical value, with a measured value of 27% compared to the theoretical value of 31.45%. The theoretical thermal efficiency can be closer to the experimental efficiency if the combustion losses caused by incomplete combustion of the fuel are taken into account.